1. Field of the Invention
The present invention relates to stethoscopes, and particularly those which filter a portion of the sound spectrum transmitted to the user.
2. Description of the Prior Art
In its most basic form, a stethoscope provides for a column of air extending from a body wall of a person to the ears of a user to transmit acoustical energy or sound. It is sometimes desirable to have a stethoscope which is capable of transmitting selected portions of the full range of sound passing through the stethoscope, such as a high frequency portion or a low frequency portion of the sound resulting from the movement of the body wall. A stethoscope which transmits selected portions of the full range of sound may better enable the user to detect various sounds in one frequency range by attenuating sounds of other frequency ranges that may mask the very sounds the user is trying to detect.
One such selective frequency stethoscope is disclosed in Canadian Pat. No. 951,247 wherein the user may rotate a portion of the stethoscope chestpiece to selectively transmit the full frequency range of sound generated or low or high frequency portions thereof. The drawback of the disclosed stethoscope is that the filtering apparatus is located in the chestpiece and is, therefore, distantly removed from the ear pieces of the user. Thus, environmental noise transmitted to the tubing of the stethoscope connecting the chestpiece and the ear pieces does not pass through the filter and is not removed or attenuated.